During manufacture of semiconductors and semiconductor microcircuits, it is frequently necessary to coat the materials from which the semiconductors and microcircuits are manufactured with a polymeric organic substance, generally referred to as a photoresist, e.g., a substance which forms an etch resist upon exposure to light. These photoresists are used to protect selected areas of the surface of the substrate, e.g. silicon, SiO.sub.2 or while such etchant selectively attacks the unprotected area of the substrate. Following completion of the etching operation and washing away of the residual etchant, it is necessary that the resist be removed from the protective surface to permit essential finishing operations.
It is necessary in a photolithographic process that the photoresist material, following pattern delineation, be evenly and completely removed from all unexposed areas, in the case of positive resists, or exposed areas in the case of negative resists, so as to permit further lithographic operations. Even the partial remains of a resist in an area to be further patterned is undesirable. Also, undesired resist residues between patterned lines can have deleterious effects on subsequent processes, such as metallization, or cause undesirable surface states and charges.
A common method used in removing the photoresist from the substrate is by contacting the substract with an organic stripper. Heretofore these organic strippers have been composed of various components whose purpose it was to lift and remove the polymeric photoresist from the substrate. However, these stripping solutions have heretofore usually contained chlorinated hydrocarbon compounds which resulted in a distinct disadvantage due to the toxicity as well as pollution problems arising from their disposal.
Chlorinated hydrocarbons-free strippers are described in U.S. Pat. No. 4,070,203 (issued Jan. 24, 1978 to Neisus et al). These strippers, having only an alkylbenzenesulfonic acid component of 12-20 carbons and a chlorine-free, aromatic hydrocarbon component with a boiling point about 150.degree. C., suffer from the disadvantage that they cannot be easily rinsed off the inorganic substrate after stripping with temperatures that are generally required for conventional stripping compositions. Moreover, such compositions are corrosive to many conventional photoresists.
It is highly desirable that stripping compositions be provided that are effective and efficient stripping compositions for removal of coatings from substrates that heretofore have resisted ready removal with conventionally available strippers.
It is also desirable that effective stripping compositions be provided that are devoid of undesirable chlorinated components and which do not require the use of hot caustic components. Highly desirable are stripping compositions and use thereof that are not considered undesirable by regulatory agencies overseeing their production and use.
U.S. Pat. No. 4,165,294 to John E. Vander Mey discloses a stripping solution free from chlorinated hydrocarbons comprising a surfactant, an alkylarylsulfonic acid and an aromatic hydrocarbon having a boiling point above 150.degree. C. The aromatic hydrocarbons are optional and are preferably mixtures of aromatic solvents having 9-13 alkyl carbons and do not comprise more than 40 weight percent. The composition does however cause pitting in many photoresist substrates.
U.S. Pat. Nos. 4,426,311; 4,395,348; 4,304,681; 4,221,674; 4,215,005 and 4,165,295 each disclose the use of an organic sulfonic acid in a photoresist stripping composition. However, the organic sulfonic acid is utilized in combination with solvents having the aforementioned disadvantages.
U.S. Pat. No. 4,992,108 to Ward et al, which is herein incorporated by reference, discloses non-aqueous biodegradable negative photoresist stripping compositions which contain an aromatic solvent and an organic sulfonic acid. The present invention provides a specific improvement over the formulations disclosed therein. The compositions in this patent cannot be used on some conventional photoresist substrates for prolonged periods because of their corrosive effects.
It is an object of the invention-to provide a non-aqueous negative photoresist stripping composition which can be used at a wide range of operating conditions and at lower temperatures without corrosion of the photoresist substrate.
It is another object of this invention to provide a photoresist stripping solution which is essentially free of naphthalene and chlorinated hydrocarbon compounds.
It is an additional object of this invention to provide such a solution which is substantially clean water rinseable such that the hydrocarbon solvent does not oil out and the polymer does not reprecipitate during rinsing.